Methods of manufacture which involve the machining of an article from homogeneous material have, in large measure, given way to modern manufacturing techniques wherein an end product is produced by bonding a plurality of constituent components under conditions of elevated pressure and often, elevated temperature. By way of example, airfoils such as those employed in aircraft propellers are often manufactured from high strength composite constituents such as plies of fiberglass reinforced expoxy resin which are layed up and then bonded together within a mold having a cavity corresponding to the desired airfoil geometry. Recently, diffusion bonding of composites such as boron reinforced aluminum has received attention as an alternative to the machining of airfoils such as gas turbine engine fans, from high strength metals.
Those skilled in the art will recognize that the application of insufficient bonding pressure to portions of a composite lay-up in a diffusion bonding process, will result in weakened areas in the product produced thereby. Uniformity in bonding pressure is a function of conformity of the lay-up to a predetermined, nominal shape. Therefore, nonuniformity in the thicknesses of the composite constituents can lead to substantial nonconformity of the lay-up to such a nominal shape and nonuniformity in the application of bonding pressure to the lay-up. Thus, variations in the thicknesses of the constituent composite plies due to normal tolerances in the manufacture thereof, can result in the application of insufficient bonding pressure to the lay-up and, therefore, inadequate structural integrity of the end product. Accordingly, in manufacturing processes such as the diffusion bonding of metallic composites wherein an assembly of constituents are bonded together within a mold under conditions of elevated pressure, a mechanism for evenly distributing bonding pressure in the face of deviation in constituent dimensions from nominal dimensions, is required.